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🧠 Why You’re Seeing This Error

The C2782 error means you’ve tried to use a function template, but the compiler can’t figure out what type to use for one (or more) of the template parameters — because those types aren’t mentioned in the function’s parameter list.

In simple terms:

C++ is saying “You gave me a template, but I don’t know what type to fill in for it.”

In UE5, this often shows up when:

• You’re using a templated helper function (like TSubclassOf<>, Cast<>, or a custom template)
• The template type can’t be inferred from the arguments
• You forgot to explicitly provide the type

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💥 Example Error Message

error C2782: 'T * MyTemplateFunction()' : template parameter 'T' is not used in parameter list

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🛠️ Example Code

template
T* SpawnActor()
{
    return GetWorld()->SpawnActor();
}

void BeginPlay()
{
    AMyActor* Actor = SpawnActor(); // ❌ C2782: compiler can't infer T
}

Here, T isn’t used in the arguments of SpawnActor(), so the compiler can’t figure out what T is supposed to be.

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✅ How to Fix C2782 in UE5 – Step-by-Step

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✔️ 1. Explicitly Specify the Template Type

Since the compiler can’t deduce the type, you need to give it manually.

Fix:

AMyActor* Actor = SpawnActor(); // ✅ Tell it what T is

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✔️ 2. Or Redesign Your Function to Use the Type in the Parameter List

If possible, pass an argument that includes the template type, so the compiler can infer it.

Fix:

template
T* SpawnActor(FVector Location)
{
    return GetWorld()->SpawnActor(Location);
}

AMyActor* Actor = SpawnActor(Location); // ✅ Now T can be inferred

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✔️ 3. Common UE5 Example – TSubclassOf<>

You might also see this error when trying to spawn a Blueprint class using TSubclassOf<>.

Wrong:

SpawnActorFromClass(MyActorBPClass); // ❌ Compiler doesn’t know the type of T

Fix:

SpawnActorFromClass(MyActorBPClass); // ✅ Template type is now clear

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✅ Summary: How to Fix C2782 in UE5

Cause	Fix Example
Template parameter can’t be inferred	Provide it explicitly: SpawnActor<AMyActor>()
Type not used in parameters	Refactor to use T in parameter list
UE5 helper template (Cast, SubclassOf)	Always specify the type when it’s not obvious